A polymer fuel cell stack (hereinafter also simply referred to as “fuel cell stack”) includes a cell assembly in which multiple unit fuel cells are stacked and connected in series. Each unit fuel cell is composed of a membrane electrode assembly (hereinafter also referred to as “MEA”) and a pair of separators arranged at both sides of the MEA. The MEA includes a polymer electrolyte membrane and a pair of catalyst electrodes (fuel electrode and air electrode) arranged at both sides of the polymer electrolyte membrane. The separator includes gas channels for supplying fuel gas or oxidizing gas to the MEA. The separator further includes a coolant channel for allowing a coolant to flow for controlling the temperature of the fuel cell stack under operation. Respective unit fuel cells are electrically connected via the pair of separators.
Further, in the fuel cell stack, in order to ensure sealing between unit fuel cells and decrease contact resistance between unit fuel cells, a pressure is applied in the direction along which the unit fuel cells are stacked (hereinafter also referred to as “fastening pressure”).
In recent years, a method is suggested for manufacturing separators by pressing metal plates into a wave shape. The separator manufactured by pressing a metal plate is called a metal separator.
As described above, the separator includes channels for allowing reaction gases (fuel gas and oxidizing gas) and a coolant to flow. Because fuel gas, oxidizing gas, and a coolant need to be supplied to their respective separate channels, a fuel cell stack includes sealing members for hermetically sealing the channels so as to prevent the respective channels from communicating with one another (for example, see Patent Literatures 1 to 8).
According to Patent Literatures 1 to 7, sealing members are stacked between an MEA and a separator and between adjacent separators to seal in reaction gases and a coolant. However, fuel cell stacks disclosed in Patent Literatures 1 to 7 have a disadvantage of deviating the relative position of separators or deviating the positions at which sealing members are arranged.
A technique for overcoming such a problem is shown in FIG. 1 (for example, see Patent Literature 8). FIG. 1 is a cross-sectional view of an end of a pair of metal separators disclosed in Patent Literature 8. In FIG. 1, in a fuel cell stack, adjacent two metal separators (first metal separator 1 and second metal separator 2) and sealing member 10 are integrated. First metal separator 1 includes corrugated plate section 5 and flat plate section 6, and second metal separator 2 includes corrugated plate section 7 and flat plate section 8. Flat plate section 6 is not in contact with flat plate section 8, and a sealing member is arranged between them.
As described above, by integrating metal separators and a sealing member, it is possible to prevent the positions at which sealing members are arranged from being deviated, improving reliability of sealing. Further, by integrating metal separators and a sealing member, the relative position of the metal separators can be fixed, facilitating easier assembly of a fuel cell stack.
However, in a pair of separators integrated with a sealing member with the sealing member being arranged between flat plate sections 6 and 8 such as that shown in Patent Literature 8, when a fastening pressure is applied to sealing member 10 in the arrow direction, ends of metal separators 1 and 2 may be deformed and thus metal separators 1 and 2 may be deformed as shown in FIG. 2. When the metal separators are deformed, sealing reliability may decrease and contact resistance between unit fuel cells may increase. For this reason, in a fuel cell stack having a pair of separators such as that disclosed in Patent Literature 8, reaction gases and a coolant may leak to outside or electrically-output of the fuel cell stack may lower.
To overcome this problem, in adjacent fuel cell stacks, flat plate sections of metal separators may be arranged on top of each other so as to be in contact with each other (for example, see Patent Literature 9).
FIG. 3 is a partially enlarged view of a cross section of a fuel cell stack disclosed in Patent Literature 9. As shown in FIG. 3, in a fuel cell stack disclosed in Patent Literature 9, flat plate sections of a pair of adjacent metal separators 30 are in contact with each other, without a sealing member being arranged between the flat plate sections. By making flat plate sections of a pair of adjacent metal separators in contact with each other in this way, the separators are prevented from being deformed even when a pressure (fastening pressure) is applied to the fuel cell stack in the direction along which cells are stacked.
Further, in the fuel cell stack shown in FIG. 3, a pair of adjacent separators 30 adhere with adhesive 28, and separators 30 and an MEA also adhere with adhesive 28.